In power engineering it is a common goal to achieve within a limited volume a transfer of energy between a gas flow and a solid body or a chemical reaction in a gas aided by a catalyst fixed to the surface of a solid body. The solid body must then be shaped with a maximum contact surface with the gas flow without too high flow resistance. The solid body is then often shaped with a large number of parallel channels, separated by thin walls, thereby dividing the gas flow into a large number of partial flows with turbulent flow pattern.
Examples of use of such flow dividers are found among heat exchangers, mufflers, catalyst carriers for chemical industry and for emission control in vehicles. Other examples are for gas flow direction in furnaces, burners and wind tunnels.
For use at high temperatures above 700 degrees C. two types of material are mainly used, none fully satisfactory.
Ceramic materials, such as aluminium oxide, can be extruded as a slurry to form bodies with parallel channels as disclosed in patents EP 294.106 and EP 275.162, and thereafter be converted by heat treatment to water-free alumina, but have disadvantages due to built-in stresses, fragility, difficulty in handling prior to the heat treatment and difficulty to shape the channel entries for low flow resistance. They may need complex mounting devices for enclosure in metal, as shown in U.S. Pat. No. 3,966,419.
Metals are easy to shape, both by extrusion and by winding together grooved, corrugated or pleated strips as shown in U.S. Pat. No. 4,719,680, but at elevated temperatures they are mechanically unstable by creep deformation, and chemically unstable by reaction with the gases.